000 FXUS61 KLWX 200135 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 935 PM EDT Mon Apr 19 2021 .SYNOPSIS... High pressure will build along the Mid-Atlantic coast tonight and Tuesday. A strong cold front will cross the area Wednesday. Canadian high pressure will build to from the west Wednesday night through Thursday before settling to the south late in the week. Low pressure may affect the area over the weekend. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... Dry conditions are expected everywhere tonight as subsidence is taking over behind the departing the disturbance. There may be some fog, especially in areas that received heavier rainfall (central VA to southern MD). However, most guidance isn't latching on to fog just yet, probably due to a light but persistent south flow. Min temps will be in the 40s for most places tonight to near 50 in downtown Washington and Baltimore. Some upper 30s are possible in colder valleys. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY NIGHT/... High pressure will remain off the Mid-Atlantic Coast Tuesday while a trough digs over the central CONUS and Midwest along with its associated cold front. A southerly flow between these systems will develop by afternoon. Along with what should be a fair amount of sunshine, temperatures should reach the 70s in many locations. Moisture return could result in an isolated shower over the Appalachians by late afternoon, but most areas will be dry. The cold front will approach Tuesday night as the upper-level trough strengthens a bit. Most of Tuesday night should be dry, but a few showers are possible, especially across western areas closer to the front. Tuesday night will turn out mild due to the southerly flow ahead of the approaching cold front. The potent upper-level trough will dig overhead Wednesday through Wednesday night. The surface low associated with this will strengthen and track to our north while a cold front passes through our area Wednesday before moving offshore Wednesday evening. Showers will likely develop along the front (with a possible minimum in the immediate lee of the Appalachians during the morning), with some embedded thunderstorms possible as the front encounters higher instability east of the Blue Ridge during the midday hours. The forcing along the front will be strong, so a line of gusty showers are possible with the frontal passage mainly east of the Blue Ridge and Catoctin Mountains, and the highest chance will be closer to the Baltimore metro where forcing/instability will ultimately be highest. The severe weather threat will be dependent on the timing of the front. Currently, the timing is fairly fast, resulting in limited instability. However, subtle changes could result in a greater risk of strong/damaging winds with the showers and storms, so stay tuned. Regardless of precipitation, strong west to northwest winds will follow the frontal passage, and temperatures will start falling. Frequent gusts around 25 to 40 mph are expected, and it's not out of the question a Wind Advisory could be needed for some areas. Any lingering precipitation along/west of the Allegheny Front could start mixing with/changing over to snow. Accumulations will be minimal, however. The upper-level trough will remain overhead Wednesday night allowing for more blustery and chilly conditions for this time of year. A few mountain snow showers are possible, and isolated snow or rain shower may even spill east of the mountain. Any accumulation should be light due to limited moisture and confined to the ridges. Min temperatures will end up in the lower and middle 30s for most places with 20s in the mountains. Freeze headlines may be warranted. && .LONG TERM /THURSDAY THROUGH MONDAY/... An anomalous upper-level trough will linger overhead most of Thursday before finally moving offshore Thursday night. Forecast 850 mb temps are -5 to -9 C much of Thursday. At the surface, this translates to highs in the 50s for much of the region, with upper 30s and low 40s across the higher terrain. The well below normal April temperatures coupled with blustery WNW winds will make it feel like late February or early March. A few lingering upslope snow showers are possible Thursday morning across the higher ridges of the Allegheny Front. Temperatures rebound closer to average Friday due to a return flow as high pressure builds to the south. Friday should remain dry. Remaining seasonable on Saturday as the region of high pressure moves offshore. The next system moves in Saturday night as an upper-level trough swings east into the Great Lakes. Ensemble guidance is in agreement with a region of low pressure forming ahead of the trough and moving either over or just south of the region Saturday night into Sunday. This system could be one of the bigger rain producers in recent weeks with ensemble guidance showing 0.50-1.00" areawide. The exact track of the low will ultimately determine QPF amounts, but there is some Gulf moisture to work with. Do not currently anticipate widespread flooding issues due to preceding dry conditions. Strong winds are also possible with this system. Temperatures will not decrease behind this system as much as the Wednesday/Thursday system due to the Pacific roots of this system. && .AVIATION /02Z TUESDAY THROUGH SATURDAY/... VFR conditions are expected most of the time tonight through Tuesday night. Low clouds and fog cannot be ruled out late tonight, especially at DCA/BWI/MTN, but guidance remains fairly strongly against it, as southerly flow has already developed and may help keep it mixed enough to limit low level moisture pooling. A strong cold front will pass through Wednesday, likely bringing some showers and perhaps even a thunderstorm (best chance across the I-95 corridor). Gusty winds are expected behind the cold front later Wednesday into Wednesday night. Frequent gusts of 25 to 35 knots are expected during this time. VFR conditions at the terminals Thursday and Friday with a gusty westerly wind. && .MARINE... The gradient has weakened for tonight and will remain weak through Tuesday morning, but winds should pick up out of the southwest Tuesday afternoon through Tuesday night. An SCA is now in effect for portions of the waters during this time. Gusty west to northwest winds are expected behind a strong cold front Wednesday afternoon into Wednesday night and a Gale Watch is now in effect. There's also potential for a line of gusty showers/isolated thunderstorms around midday Wednesday with the cold front. Gales may persist at times Thursday, so Gale Watch includes Thursday. SCA conditions could last into Friday as a weaker, but still gusty southerly wind develops. && .TIDES/COASTAL FLOODING... Anomalies have declined some this evening, but likely rise again with returning southerly flow late tonight and Tuesday. Water levels could reach caution stages for sensitive areas with the high tide cycles Tuesday and Wednesday mornings. Minor flooding cannot be ruled out, but confidence is low due to the light flow. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Gale Watch from Wednesday afternoon through Thursday afternoon for ANZ530>543. Small Craft Advisory from 3 PM Tuesday to 6 AM EDT Wednesday for ANZ532>534-539>541-543. Small Craft Advisory from 6 PM Tuesday to 6 AM EDT Wednesday for ANZ531-537-538. Small Craft Advisory from midnight Tuesday night to 6 AM EDT Wednesday for ANZ530-536-542. && $$ SYNOPSIS...ADS/RCM NEAR TERM...ADS/RCM SHORT TERM...ADS LONG TERM...CPB AVIATION...ADS/CPB/RCM MARINE...ADS/CPB/RCM TIDES/COASTAL FLOODING...ADS/RCM